The invention relates in general to fine liquid mist fire protection/suppression systems for fire extinguishment. In particular, the invention relates to an effervescent fine liquid mist-type system that uses chemical reactions to produce a bubbly two-phase flow output through a nozzle or array of nozzles.
Fluorocarbon-based fire extinguishants are environmentally harmful because they cause depletion of the earth""s ozone layer. Present U.S. law and treaty requires the phase out and replacement of such materials under the 1988 Montreal Protocol, which classified Halon as a Class I Ozone Depleting Substance (ODS), and which called for limits on global production by over 100 developed nation signatories. Furthermore, the U.S. Clean Air Act Amendments of 1990 call for the ban on production of Halon in the U.S after January 1994. This law also prohibits purposeful venting and requires training personnel involved with their use to minimize their emission into the atmosphere. The U.S. Navy has responded to the requirements of these acts by prospectively prohibiting the use of ODSs and by finding and using alternative designs in fire extinguishment systems. Therefore, a need exists to replace all halon systems and improve existing water sprinkler based systems for more effective fire extinguishment use.
Fine liquid mist type systems have very favorable characteristics as a replacement for existing Halon systems. Typically, such systems include nozzles for creating misting fluids using a pressurized gas and such type systems are well-known. A liquid is injected into a central bore of a nozzle that directs a high-velocity gas. In some nozzles, the velocity and pressure of the gas are increased in a narrowed throat area of the bore, which causes atomization of the fluid into small droplets as the gas travels through the nozzle. To aid atomization and provide an unobstructed flow path for the gas, the fluid is usually injected into the gas stream through an aperture in the bore wall so that the two different fluid streams impinge at a 90-degree angle. Nozzles of the above-described type require high-pressure spraying of the liquid and the gas, which is undesirable. Another problem with these mixing nozzles is that the liquid and gas must be sprayed through fine holes of a small diameter, which can easily clog or wear away.
The use of water as a spray for fire extinguishment is well-known. Liquid-only, water spray nozzles for fire extinguishment create water droplets by deflecting the water flow just ahead of the spouting aperture. The droplet""s size is relatively large and a desirable fine water mist cannot be achieved. The need for a low-pressure, reliable, liquid/gas mixing nozzle which is effective for fire extinguishment is disclosed in U.S. Pat. No. 5,520,331 issued on May 28, 1996 to Joseph E. Wolfe and entitled xe2x80x9cLiquid Atomizing Nozzlexe2x80x9d, which patent is hereby expressly incorporated by reference. In the ""331 patent, the nozzle structure effects an extremely fine, liquid atomization with low pressurization of the liquid and gas that are delivered to the nozzle. Furthermore, the fluid and gas are delivered through relatively large apertures so that wear and clogging are minimized. The ""331 patent also discloses a convergent/divergent (C-D) gas nozzle affixed to a mixing block having a liquid delivery tube with an aperture that is centered within a gas conduit and located just upstream of a narrowed throat of the nozzle.
One aspect of the invention is an apparatus comprising a container capable of holding fluid; one of a perforated basket and a porous bag disposed in the container; a liquid supply connector connected to the container; a mixing chamber connected to the container; and at least one convergent/divergent nozzle connected to the mixing chamber. The apparatus further comprises a chemical reactant disposed in one of the perforated basket and the porous bag.
Another aspect of the invention is a method of forming an effervescent fine liquid mist comprising mixing liquid and chemical reactant to form non-toxic, noncombustible gas bubbles; mixing the liquid and the gas bubbles to form a two-phase fluid flow; and directing the two-phase fluid flow through at least one convergent/divergent nozzle. Preferably, the directing step includes directing the two-phase fluid through a plurality of convergent/divergent nozzles.
The method further comprises, after the directing step, expanding the gas bubbles in a diverging section of the nozzle. The method further comprises, after the expanding step, shearing the liquid to form a liquid mist.
Another aspect of the invention is an apparatus comprising a first container, the first container including pressurized liquid disposed therein; a second container disposed in the first container, the second container including a chemical reactant disposed therein, the second container including a gate having a closed position for isolating the pressurized liquid from the chemical reactant and an open position for allowing the pressurized liquid to enter the second container; a mechanism for opening and closing the gate in the second container; a mixing chamber connected to the second container; and at least one convergent/divergent nozzle connected to the mixing chamber.
Further objects, features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the following drawing.